1. Field of the Invention
This invention relates to a digital video recording apparatus which encodes a digital video signal and an audio signal and employs an audio encoding control technique when an audio encoding condition is changed in a digital video recording apparatus.
2. Description of the Related Art
In recent years, a digital video recording apparatus, which digitally encodes a video and an audio signal and stores both, has come into practical use as the storage capacity of optical and hard disks has increased.
The audio signal may be classified into a stereo (two channels), a monaural (one channel), and a multiplex (main voice: one channel+sub-voice: one channel) sound signal. An audio signal has 5.1 channels in the standard of Dolby AC-3 or linear PCM. In a digital audio stream, picture/sound recording time can be controlled, or sound quality, when reproduced, may be controlled by changing an encoding bit rate.
Referring now to FIG. 4, a time-dependent change is shown in audio output level intensity when such an encoding condition (stereo, monaural, multiplex, number of channels, and bit rate) is changed in a conventional digital video recording apparatus. Here, the horizontal axis indicates time, and the vertical axis indicates a constant output intensity of an audio level.
When the audio encoding condition is changed at a time t in the conventional digital video recording apparatus, the condition is changed while keeping the audio output level intensity fixed both before and after the change.
The present inventors have found that the audio signal becomes discontinuous before time t and after time t. When the audio signal is reproduced, an undesirable cacophonous noise, which is called a “puff sound”, is generated when the audio encoding condition (stereo, monaural, multiplex, number of channels, and bit rate) is changed in the digital video recording apparatus. The related art does not take measures to prevent this kind of noise.